I have an application with different QML documents, of which some are loaded via Loaders. There is also one JS wile with ".pragma library". The QML files share data via that JS file.

This works well in non-compiled QML or when using the qtquickcompiler 1.1 (shipped with Qt 5.3). But when using the qtquickcompiler 2.0 (shipped with Qt 5.4), some QML files see different data in the JS file.

Here the minimal example followed by its output:

source.js:

.pragma library
var string = undefined;

A.qml:

import QtQuick 2.3
import "source.js" as Source
Item {
    Component.onCompleted: {
        Source.string = "Foo";
        console.log('A.qml set the string: ' + Source.string);
    }
}

B.qml:

import QtQuick 2.3
import "source.js" as Source
Item {
    Component.onCompleted: {
        Source.string += "Bar";
        console.log('B.qml appended a string: ' + Source.string);
    }
}

main.qml:

import QtQuick 2.3
import QtQuick.Window 2.2
import "source.js" as Source
Window {
    visible: true; width: 360; height: 360

    Loader { source: "B.qml" }
    Loader { source: "A.qml" }
    Component.onCompleted: {
        console.log('main.qml read the result: ' + Source.string);
    }
}

Output with qtquickcompiler 1.1 or non-compiled QML:

qml: A.qml set the string: Foo
qml: B.qml appended a string: FooBar
qml: main.qml read the result: FooBar

But in the faulty case, it does this:

qml: A.qml set the string: Foo
qml: B.qml appended a string: FooBar
qml: main.qml read the result: undefined

main.qml seems to have access to another "instance" of the JS file.